Aircraft supercharger control



l Y `A. G. SILVESTER AIRCRAFT SURRRCHARGER CONTROL June -19, 1945.

Filed Feb. 21 1942 ,maak-...IE

--Ihventorz Ausoi'w (i. Svester,

Patented June 19, 1945 l AIRCRAFT SUPERCHARGER CONTROL Austin G. Silvester, Swampscott, Mass.,`assignor to General Electric Com New York pany, a corporation of Application February 21, 1942, Serial No. 431,861

' 1a claims. (o1. io-13) The present invention relates to aircraft supercharger control for superchargers of the type comprising a gas turbine driven by exhaust gases froman aircraft engine. In such installations, the exhaust manifold of the aircraft engine is connected by a conduit to the nozzle box of the gas turbine and the primary control is'eflected by meansof a Waste gate valve connected in parallel with the nozzle box and controlling flow of exhaust gases from the exhaust manifold directly to atmosphere. When the waste gate valve is wide open, the exhaust gases discharge directly to atmosphere. 'Ihe nozzle box pressure is then equal substantially to atmospheric pressure so that but little gas flows from the nozzle box through the turbine nozzles to the turbine Wheel. c The turbine wheel may then be turning at`what may be termed idling speed. As the waste gate valve is moved -toward closed position, the exhaust gas pressure in the nozzle box is gradually built up so that more and more gases are directed through the turbine Wheel, the maximum condition being reached I when the waste gate valve is fully closed. 'I'he 'power delivered tothe turbine wheel is a function of the drop in pressure across the wheel, i. e., the difference between nozzle box pressure and atmospheric pressure.

It is now the usual practice to control the waste gate valve by nozzle box pressure, the control being set for a certain nozzle box pressure, and automatically maintaining such pressure with changes in altitude. Due to changes in atmos-V pheric pressure with changes in altitude, this serves to effect changes in the supercharger speed, the speed increasing with increase in altitude and decreasing with decrease in altitude. However, this does not give constant power outputof the aircraft engine, the thing desired, but actually results in an increase in power output with increase 'in altitude. -1 type, if the operator is to maintain constant power output, he must adjust his control for lower and lower nozzlebox pressures with increase in altitude. In addition, if the operator increases his altitude above rated altitude of the supercharger, he must decrease the nozzle box pressure and the engine power output to prevent overspeeding of the supercharger. v l

The object of the present invention is to provide 'an improvedsupercharger control wherein the control is e'fected primarily by nozzle box pressure but 'such control is` modified automatically to maintain substantially constant engine power output up to rated supercharger altitude after 55 As a result, with a control of this` which it maintains rated supercharger output, the engine power output decreasing.

For a consideration of what I believe to be novel and my' invention, attention is directed to the following specication and the claims appended thereto.

In the drawing, Fig. 1 isa diagrammatic view of a supercharger control system embodying my in ventlon and Figs. 2 and 3 are diagrams.

Referring to the drawing, I indicates a portion of an aircraft in which is enclosed an aircraft engine which drives a propeller 2. Associated with the engine is a supercharger comprising a gas turbine 3 and a centrifugal compressor 4. Exhaust'l gases from the aircraft engine are-supplied to nozzle box 5 of the gas turbine through a conduit 6. Connected to the nozzle box is a waste conduit 1 in which is located a Waste gate valve 8 which forms the control means for the gas turbine. Air is supplied to the compressor 4 through a conduit 9 and is discharged from the compressor through a conduit I0 which conveys the air through an intercooler Il and a carburetor l2 to the aircraft engine intake.

The operation of an exhaust gas driven supercharger is known and req-uires no detailed expla nation.

Exhaust gases from the aircraft engine are supplied to the nozzle box and discharged from the nozzles in the nozzle box against the turbine wheel to effect its rotation and driving of the centrifugal compressor. Waste conduit 1 discharges directly to atmosphere. When Waste gate valve 8 is open; conduit 1 permits the exhaust gases supplied to the nozzle box to exhaust directly to atmosphere, little, if any. passing through the nozzles to the turbine wheel. This represents idle operation of the supercharger.' As waste gate valve B is moved toward closed position, more and more of the exhaust gases are caused to flow through the nozzles to the turbine wheel. closing of the waste gate valve building up exhaust gas pressure in the nozzle box. When Waste gate valve 8 is completely closed, all the gases are then discharged to the bucket wheel which represents maximum load on the supercharger. A

On one end of the valve spindle of waste gate valve 8 is fixed an arm I3 pivotally connected to one end ofthe 'piston rod I4 of azfluid actuated servo-motor which has a piston I5 and a cylinder I6 controlled by a pilot valve-l1.4 The stem I8` of the pilotvalve is pivotally vconnected to an innectedto piston I5. This forms a usual type of follow-up connection for the servo-motor. The inlet pipe through which fluid pressure is supplied to the pilot valve is indicated at 22 and the outlet pipes at 23 and 24. The pilot valve heads aredndicated at 25 and 2B.

Movable abutment 20 is subjected to and arranged to be positioned by the absolute pressure obtaining in the nozzle box. Any suitablemeans may be used for this purpose. In the present instance, abutment 20 has on one side an evacuated bellows 21 mounted on a fixed support 28 and on the other side a bellows 29 mounted on a -xed support 30, the interior of bellows 28 being connected to the nozzle box by a pipe 3|. Thus, the upper surface of abutment 20 is subjected to absolute nozzle box pressure.

Connected at one end to abutment 20 is a tension spring 32, the other end of which is connected to an end of a rod 33 which projects with a sliding fit through an opening in the top wall of bellows 23. The upper end of rod 33 is pivotally connected to an intermediatepoint on a 'floating lever 34. One end of floating lever 34v is piv- 'otally' connected to one arm of a bell crank lever 35, the other arm of which is connected by a link to a hand lever 31 adjusted over a quadrant 3&3. Surrounding rod4 33 is a compression spring 33 which at its upper end engages an adjustable abutment 40 on rod 33 and at its other end a fixed support 4l having an opening through which rod 33 freely passes. Spring 39 acts in opposition to spring 32 and serves to compensate for a major portion of the pull of spring 3 2 on rod 33. Spring 32 is normally under considerable tension and spring 39 prevents the entire tension of spring 32 from being applied to the lever mechanism. The lower end of rod 33 forms a normally fixed support for the upper end of spring 32, rod 33 being normally held in a fixed position to which it has been adjusted.

vAssuming that. the left hand end of lever 34 is fixed, it will be seen that by adjusting hand lever 31 along quadrant 33, rod 33 can be raised or loweredto increase or decrease the tension of spring 32, thus changing the setting of the regulator vcomprising abutment 2lil Each setting of spring 32 corresponds to a certain nozzle box pressure so that by adjusting the tension oi spring 32, the

nozzle box pressure for which the governor is set can be varied. Having been set fora. certain nozzle box pressure, such pressure will be maintained automatically by the regulator. II the pressure tends to increase,the increased pressure acting on the upper surface of abutment 2l will lower the abutmentagainst the action of spring 32 (rod 33 being stationary) andl acting through the uid operated servo-motor will open some- 'what waste gate valve 8. Dpening of waste. gate valve 8 permits more of the exhaust gases to escape directly to atmosphere which results in a. decrease in nozzle box pressure. AIn a similar manner, waste gate valve 3 is closed somewhat if the nozzle box pressure tends to decrease.

Assuming now a condition of changing altiordinates nozzle box pressure, supercharger speed. and engine horse power, it will be seen that constant nozzle box pressure represented by line a results in increase in horse power with increase in altitude as represented by line b; also, it results in continuously increasing supercharger speed as represented by line c. In Fig. 2, vertical line d represents rated supercharger speed, or what may be termed the critical altitude of the supercharger, i. e., the altitude up to which the supercharger is designed to maintain full engine horse power.` Beyond this altitude, the supercharger must be operated at above its rated speed if constant nozzlebox pressure is maintained.

According to my invention, I provide in connection with the control for the supercharger, automatic means for modifying its setting so as to maintain a desired load characteristic on the aircraft engine with change in altitude, for example, constant engine horse power, up to rated altitude for the supercharger,` i. e., up to rated supercharger speed, and thereafter maintain rated supercharger speed.

A desirable condition of operation is represented in Fig. 3, for example, wherein constant engine horsepower is maintained up to critical supercharger altitude as represented by line b1, b2 after which constant supercharger speed is main-- tained as represented by line c2, c3. To obtain tude, as the aircraft ascends., v.the supercharger must be operated Iat higher and biglie!" speeds in order to maintain engine horse power.v This result is effected by the gradual closingfof waste gate valve 3 'maintain substantially constant nozzle box pressure. However, as already pointed out, substantially constant nozzlebox pressure does not result in substantially constant engine horsepower. Referring to Fig. 2, for "example, wherein the abscissarepresent altitude-and the this result,. the nozzle box pressure decreases gradually up to critical supercharger altitude along the line a1, a while the supercharger speed gradually increases along the line c1, c2. Above critical supercharger altitude, the supercharger speedremains constant while the nozzle box pressure'decreases along line a2, a3 and the engine horse power decreases along the line b2, b3.

'Referring now to Fig. 1, the left hand end of floating lever 34 is pivotally connected by a link 42 to an arm 42' fixed on the end of the shaft of a reversing motor 43. The end of lever arm 34 is provided with a numberof openings 34' into any one of which link 42 may be connectedto adjust the effective length of the lever arm. The common lead of motor 43 is connected by a conductor 44 to one side of a source of electrical energy 45 and the other two leads are connected by conductors 46 and 41 to two spaced contacts 48 and `43 carried in a circuit closer housing 50. Housing housing 50 and sealed to the housing by a flexible bellows 54 is a contact rod 65 having an @miV which lies between contacts 48 and 49. Contact rod 55 is connected by a conductor 36 to the other side of the source of current 45.

' The outer end of rod 55 is connected to the -head 51 of a pressure responsive device comprising a primary evacuated bellows 58 and a secondary evacuated bellows .'3v separated from each other by a wall 6.0 and mounted on a fixed support 6I. Located between support 3i and wall 30 is a compressionfA` spring 82 which acts in a direction to ,distendgbellows 53 and locatedI between wall 30 and head 5-1 is a compression spring 33 which acts in a direction to distendbellows 39. collapsing movement of the bellows is limited by stops 34 pressor and a gas driven turbine and 85 respectively and distending movement of bellows B is limited by an adjustable stopv. The pressure responsive devicey is subjected to altitude atmospheric pressure and the arrangement, including the relative strengths of the two u springs 92 and 99, is such that beginningJ at a desired altitude, primary bellows 58 is gradually distended with increase in altitude until supercharger critical altitude is reached at which time wall 80 engages stop 66, after which secondary bellows 59 is gradually distended with increase in altitude. Distension of either bellows moves contact rod 55 toward the right and into engagement with contact 49 closing a circuit on motor 43 to eiect turning of the motor shaft in a clockwise direction as viewed in Fig. 1. This lowers the left hand end of floating levcr 34, thus moving downward rod 33 to set the regulator for a lower lating the gas supply to the turbine, a regulator nozzle box pressure, the regulator acting to open somewhat waste gatel valve 8 to lachieve this result. When' the motor shaft turns in clockwise direction, cam 53 eil'ects movement of circuit closer housing 50 toward the right to open the motor circuit. 'I'he arrangement is such that with increasing altitude up to supercharger critical altitude, primary bellows 58 modifies the setting of the regulator comprising bellows 21, 29 so that it holds a nozzle vbox pressure which will give the desired engine load characteristic, for example, constant engine horse power, with increasing altitude upto supercharger critical altitude. after which secondary bellows 59 will come into action t6 modify the setting of the regulator to hold nozzle box pressuresvwhich'with increasing altitudes will maintain constant supercharger speed.

With decreasing altitude', bellows 58 and 59 act in a similar manner except in the opposite direction, contact rod 55 engaging contact 49t effect operation of motor 43 in a direction' to increase the nozzle box pressure for which the regulator is set.

By connecting'link 42 in different openings 34', the eiect o`fa given movement of the motor on the spring 92 may be varied. i

While I have particularlyK illustrated and described my invention as applied to a control system for a supercharger wherein the regulator is responsive to nozzle box pressure, it will be understood that my invention is not limited thereto but may be used in controlsystems wherein the control is responsive to operating conditions of the supercharger other than nozzle box pressure.

responsive to the pressure of the gas supplied to the turbine for positioning said rvalve means in response to any change of absolute gas pressure, manual means for adjusting the setting of said regulator, and neans responsive to altitude pressure for modifying the setting of said regulator and for limiting the speed of the turbine to maintain a desired load characteristic on the engine with variations in altitude.

3. The combination with an aircraft engine and a supercharger for the engine. of automatic means including a pressure responsive device for regulating the supercharger to maintain constant power output of the engine up to rated altitude'of the supercharger and another device connected to vthe `first mentioned device to regulate the supercharger to maintain constant speed of the supercharger Vabove said rated altitude.

4. The combination with an aircraft engine and an exhaust gas driven supercharger for supplying airthereto, of regulating means operative at all altitudes and responsive to the pressure of the exhaust gases for regulating the supercharger, and other means responsive to altitude atmospheric pressure for modifying the setting of said regulating means to maintain constant power output on the engine between ground level and a rated altitude of the supercharger and theeafter to maintain constant supercharger loa f s 5. The combination with any aircraft internal combustion engine and a. gas turbine driven supercharger for supplying air to the engine, of a regulator for the supercharger, means responsive to absolute pressure changesin the supercharger for positioning said regulator, and other In accordance with the provisions of the patent I statutes, I have described the principle of operation of. my invention, together with the apparatus which I now consider to represent the best embodiment-thereof, but I desire to have it understood that the apparatus shown isv only illustrative and that the invention may be carried out by other means. v y.

. What I claim as new and desire to Letters Patent ofthe United Statesis:

1. In combination, an aircraft internal combustion engine, a supercharger comprising a comwheel, a conduit secure,N by

for conveying exhaust the turbine, a conduit for conveying air from the compressor to the engine, valve means for regulating the gas supply to the turbine, a regulator responsive to the absolute pressure of the 'gas supplied to the turbine for positioning said valve means, and means for modifying the maintain a desired responsive to altitude pressure setting of said regulator to load characteristic on the gases from the engine to Vmeans responsive to altitudeatmospheric presl sure for modifying the setting of the first mentioned means to give a desired engine power output between ground level and supercharger critical altitude and thereafter to give constant supercharger speed.

6. The combination with an aircraft internal combustionv engine and a. gas turbine driven supercharger for supplying air to the engine of a control mechanism for the supercharger comprlsing a device responsive to any change of absolute-pressure in the supercharger, a floating lever, means including an adjustable spring connecting the device to the lever, manually operated means connected to the lever for varying said spring to vary the load output at a given altitude, and other means the'setting of of the engine connected to said absolute sponse to any change in atmospheric pressure to maintain the load output of the engine substantially constant between ground level and a certain altitude and to effects decrease of the lload output above said altitude.

7. 'I'he combination with an aircraft internal combustion engine and a gas turbine driven supercharger for supplying air to the engine of the lever to modify the action of pressure responsive device in rea control mechanism for the supercharger comprising a devicev responsive to absolute pressure changes in the supercharger, a floating lever, means including an adjustable spring connecting the device to the lever, manually operated means connected to the lever for varying the setting of said spring to vary the load output of the engine at a given altitude, and other means connected to the lever to modify the action of said absolute pressure responsive device in response to change of altitude to maintain the load output of theengine substantially constant between ground level and a certain altitude and to effect a decrease of the load output above said altitude, said other means including two atmospheric pressure responsive devices having different characteristics and one device being .operative below and the other device above said certain altitude.

8. The combination with an aircraft engine and a supercharger for the engine, of automatic means for regulating the supercharger to maintain substantially constant power output of the engine up to the rated altitude of the supercharger`and thereafter regulating the supercharger to maintain substantially constant speed of the supercharger, said means comprising a primary control mechanism for the supercharger and an auxiliary control mechanism for modifying the operation of the primary control mechanisrn including an atmospheric pressure responsive device eiective at low altitude and another atmospheric pressure responsive device eiective only at high altitude.

9..In combination, an, aircraft internal .combustion engine, a compressor for supplying air under pressure' to the engine, a. gas turbine for driving the compressor having an inlet nozzle box with a waste gate to atmosphere and being connected to receive exhaust gases from the engine, and a regulating mechanism for the waste gate comprising means responsive to any changes of absolute nozzle box pressure and other adjustable means for manually and automatically modifying the operation of said iirst mentioned means to decrease the nozzle box pressure with increasing altitude at a rate suiiicient to preclude the engine loutput from rising above a; certain sea level output and to preclude the turbine speed from rising above a predetermined value.

l0. In'combination, an aircraft internal comnozzle box pressure, vand means responsive to r changes of atmospheric pressure for modifying the operation of said device to effect decreasing nozzle box pressure with increasing altitude at' a rate to maintain the engine output up to a certain altitude substantially constant and equal to .a predetermined sea levelI output, means to vary the sea levelroutput, and other means gradually'to reduce said output above said certain altitude.

11. In combination, an aircraft internal coinbustion engine, a gas turbine driven supercharger for the engine including a gas turbine nozzle box having a waste gate and being connected to receive exhaust gases from the engine and a control mechanism for the waste gate comprising a device responsive to changes of absolute nozzle box pressure, and means for modifying the operation of said device including a first atmospheric pressureresponsive device and a second atmospheric pressurev responsive device dimensioned to effect substantially constant engine output between sea level and a predetermined altitude and substantially constant supercharger speed above said predetermined altitude.

12. In combination, a gas turbine driven supercharger for aircraft including'a gas turbine with a nozzle box having. a waste gate and a control mechanism for the waste gate comprising a device responsive to any` change of absolute nozzle box pressure, and mealns for modifying the operation of said device including a iirst atmospheric pressure responsive device operative below. a pre- AUSTIN G. SILVES'I'ER. 

